Curated Texan
Why 70% Of Everything We See, And Don’t See, Remains Unexplained, And How Astronomers At West Texas’ Hobby-Eberly Telescope Are Chasing Answers Across A Billion Galaxies
By Dr. Frank N. Bash Photography courtesy of McDonald Observatory, David Cook & Brian Fitzsimmons
The reason I am an astronomer is that I didn’t want to spend my career just adding another decimal point to what we already know. I was fascinated that the Universe throws you curveballs. You discover things that in your wildest imagination you couldn’t have anticipated. One of those is Dark Energy. I emphasize that that’s just a name. We don’t understand it.
The current picture is that the Universe was formed from a giant explosion that occurred about 13.5 billion years ago. Out of the explosion came all the matter and all the space that we currently enjoy. But picture throwing a baseball straight up into the air. The baseball feels the full force of Earth’s gravity and begins to slow down. This is just like the expanding Universe. If you throw the baseball fast enough, the gravity will not be strong enough to stop it. The baseball has reached escape velocity and will never stop. If you don’t throw it fast enough, the baseball will eventually be brought to a stop and fall back down. This is exactly how we pictured the Universe.
But Recently, Astronomers Discovered That The Expansion Of The Universe Is Speeding Up
Wow. The cause is a mysterious force called Dark Energy. Even more baffling is that Dark Energy accounts for about 70% of the Universe’s content. Dark Matter (which has gravity but no light) contributes about 25%, and “baryonic matter,” out of which all the stars and planets are made, and we are made, contributes the last 5%. So, you can see that Dark Energy is important. It is dominant.
Under the leadership of Professor Karl Gebhardt, the Hobby-Eberly Telescope (HET) was extensively modified with 34000 optical fibers feeding 156 spectrographs. Each fiber produces a spectrum. The instrument and the experiment are called HETDEX (Hobby Eberly Telescope Dark Energy Experiment). There is nothing else even remotely approaching it in the World.
The point of the experiment is to measure the expansion speed of distant galaxies to see how Dark Energy has changed over the millennia. The experiment has been completed. One billion spectra have been collected, and one million galaxies have been observed. The results have not yet been published due to the extreme effort to ensure the data have been scrubbed of false entries. The results will not be, in themselves, an explanation of Dark Energy, but will rule out certain proposed explanations. So, stay tuned for an important announcement when the results are published.
What Does It Mean To Understand Dark Energy?
Science describes, but it does not explain why the Universe is “thus and not otherwise,” or understanding what is in the “mind of God” is not what science is all about, although Einstein believed that ultimately it would be possible. Science describes what can actually be observed and measured. I emphasize describes. So as science progresses, it just refines the description.
Gravity is an excellent example. Isaac Newton described gravity as a force between two objects that acts to pull them together and whose strength depends on the product of their masses divided by the square of their distance apart. That description of gravity perfectly explained the orbits of all planets orbiting the Sun except Mercury. It was a bit off. Then along came Einstein and his theory of General Relativity. He described gravity completely differently. He said that every object with mass distorts the space around it. The stronger the gravity, the more distorted the space. Far-out planets orbit in space that’s only slightly distorted, but Mercury is a different story.
When space is distorted, light doesn’t travel in a straight line but along a curved path that is the shortest distance between two points in the distorted space. The planet Mercury orbits in the most distorted space. Einstein’s theory perfectly describes Mercury’s orbit.
So, We May Never Understand Dark Energy
And understanding it may have little effect on your life. But like general relativity, you can take satisfaction from our improved description of the Universe and marvel at what human beings can accomplish.
